Add some tests for string and NUL

tests/string.err

@@ -291,3 +291,6 @@ string repeat -l fakearg
 
 ####################
 # string match -r "a*b([xy]+)" abc abxc bye aaabyz kaabxz abbxy abcx caabxyxz
+
+####################
+# Check NUL

tests/string.in

@@ -329,4 +329,15 @@ or echo strings not converted to uppercase
 string upper -q ABC DEF
 and echo uppercasing a uppercase string did not fail as expected
 
+logmsg 'Check NUL'
+# Note: We do `string escape` at the end to make a `\0` literal visible.
+printf 'a\0b' | string escape
+printf 'a\0c' | string match -e 'a' | string escape
+printf 'a\0d' | string split '' | string escape
+printf 'a\0b' | string match -r '.*b$' | string escape
+printf 'a\0b' | string replace b g | string escape
+printf 'a\0b' | string replace -r b g | string escape
+# TODO: These do not yet work!
+# printf 'a\0b' | string match '*b' | string escape
+
 exit 0

tests/string.out

@@ -422,3 +422,14 @@ bxy
 xy
 aabxyx
 xyx
+
+####################
+# Check NUL
+a\x00b
+a\x00c
+a
+\x00
+d
+a\x00b
+a\x00g
+a\x00g